I have a suggestion; in case a key gets lost for a car, you should hide an emergency key inside. I'm talking from experience here. Any type of outside key-holding device always seems to fall off.

I was in a situation where the key got lost (long story); a spare was hidden but it got lost. You should keep a spare inside the car since you can unlock it by remote anyways. You wouldn't have to tell anyone where the key was until it was needed, or you could even have a storage case which could be unlocked by remote signal as well. Just a suggestion.